In order to provide a warning to others, vehicles such as ambulances, fire trucks and police cars (“primary vehicles”) may utilize loud sirens or flashing lights. Those warnings are generally provided for drivers of other vehicles (“secondary vehicles”). Unfortunately, these warning methods are often not effective, not being heard or seen by drivers or passengers of the secondary vehicles. Other warning means may provide warnings via the secondary vehicle radio. However, communications systems that utilize a secondary vehicle's radio are also not particularly effective, since the driver of the vehicle may not have their radio turned on.
Various prior art exists which describes signal generators and use of those signals. However, this prior art does not teach or suggest a warning signal system which is effective for use with vehicles.
U.S. Pat. No. 5,661,470 (Karr) This invention relates to LC responders and particularly to LC responders that are placed within objects such as toys. In operation, an interrogation or base unit sends a pulse and passive responders reply with their unique frequency which is sensed by the base unit triggering a particular response such as turning on a motor etc.
U.S. Pat. No. 4,023,167 (Wahlstrom) teaches a system in which bursts of radio frequency are transmitted to excite and thereby detect the presence of passive resonant circuits. If a circuit is resonant at a particular burst frequency, it is excited, rings and emits a radio frequency signal. Following each transmitted burst, a receiver is turned on to receive energy emitted by the resonant circuit so that if a resonant circuit is excited, its emitted energy is received and the particular resonant circuit can be identified.
U.S. Pat. No. 3,863,244 (Lichtblau) is an electronic security system adapted having improved noise discrimination for use in a controlled area such as a retail store and employing a multi-frequency resonance tag circuit having distinct frequencies for detection and discrimination.
U.S. Pat. No. 3,895,368 (Gordon) describes an apparatus in which a microwave signal generator projects an electromagnetic wave into a space under surveillance to establish a first field. A pulse or frequency modulated low frequency generator is used to apply a voltage to a discontinuous conductor for establishing a second field, electrostatic in nature, throughout the space. Presence in the space of a miniature, passive, electromagnetic wave receptor-reradiator in the form of a semi-conductive diode connected to a dipole antenna causes the reradiation of the low frequency component modulated on the microwave component as a carrier. The front end of a receiver system is tuned to the microwave frequency signal. A coincidence circuit energizes an alarm circuit whenever the detected signal coincides with the original modulation envelope being applied to the low frequency generator.